A display device used in a portable device such as a smart phone and a tablet PC is required to have high fineness, e.g., a pixel density of 300 ppi or more. In addition, there is increasing demand that the portable device is applicable in the full high-definitions reference. In this case, the pixel density of the display device needs to be 450 ppi or more, for example.
An organic EL display device draws attention because of its excellent responsibility and low power consumption. A known method for forming pixels of an organic EL display device is a method which uses a deposition mask including through-holes that are arranged in a desired pattern, and forms pixels in the desired pattern. To be specific, a deposition mask is firstly brought into tight contact with a substrate for organic EL display device, and then the substrate and the deposition mask in tight contact therewith are put into a deposition apparatus so as to deposit an organic material and so on.
A deposition mask can be generally manufactured by forming through-holes in a metal plate by etching using photolithographic technique (see, for example, Patent Document 1). For example, a first resist pattern is firstly formed on a first surface of the metal plate, and a second resist pattern is formed on a second surface of the metal plate. Then, an area of the second surface of the metal plate, which is not covered with the second resist pattern, is etched to form second recesses in the second surface of the metal plate. Thereafter, an area of the first surface of the metal plate, which is not covered with the first resist pattern, is etched to form first recesses in the first surface of the metal plate. At this time, by etching the areas such that each first recess and each second recess communicate with each other, through-holes passing through the metal plate can be formed.
In a deposition step using a deposition mask, a deposition mask and a substrate are arranged such that a second surface side of the deposition mask faces the substrate. In addition, a crucible storing a deposition material such as an organic material is arranged on a first surface side of the deposition mask. Then, the deposition material is heated to evaporate or sublimate the deposition material. The evaporated or sublimated deposition material adheres to the substrate through the through-holes in the deposition mask. As a result, the deposition material is deposited on a surface of the substrate, in a desired pattern corresponding to the through-hole positions of the deposition mask.    Patent Document 1: 3132014-148740A